Generally speaking, Instrument Landing Systems (ILS) are widely used in the aviation industry to provide guidance to aircraft. Specifically, ILS are often used to provide approach guidance to an aircraft for landing. The system usually consists of transmitters and antenna arrays on the ground, antennas and receivers on the aircraft, and a display for the flight crew. Autopilots and flight directors may also actively participate in the system.
A localizer component of the ILS may provide lateral guidance beams, while vertical guidance beams may be provided by a glide slope component of the ILS system. Both components provide the aircraft with an indication of its separation from the desired approach path, in the form of an angular error.
An aircraft preparing to perform a landing approach may fly a flight path which intersects the localizer. Typically, when an aircraft reaches the linear part of the localizer beam, (the course guidance sector), it executes a localizer reposition maneuver to reposition the desired approach path (the null of the localizer). In most instances, the localizer null may be configured to align with a runway centerline. Alternatively, the localizer null may be configured to indicate a particular point in space from which a flight crew may maneuver the aircraft to a corresponding runway.
Accordingly, after a successful reposition maneuver, the aircraft's flight path will generally be in line with the runway centerline or aligned with the particular point in space. Ideally, the aircraft on approach performs a single turn to reposition the localizer null, and will not fly through the null (overshoot) prior to completing its turn.
Although desirable results have been achieved using such prior art systems, there may be room for improvement. For example, localizer overshoots may occur due to the fact that the segment of the localizer beam which reliably provides an accurate indication of aircraft displacement is relatively narrow. This segment, commonly known as the course guidance sector, may be only approximately +/−2 degrees of arc about the localizer null. As a result, if an aircraft does not begin its reposition maneuver until it encounters this sector, it may have only a small distance in which to complete its turn in order to avoid an overshoot.
Additionally, an overshoot may be exacerbated if the aircraft is intercepting the localizer with a large intercept angle, a high ground speed, or is close to the airfield (where the angular beam width corresponds to a smaller physical distance). Localizer repositions with a significant overshoot may waste fuel, may cause discomfort for aircraft passengers, and may make it necessary for air traffic control to widely space incoming aircraft at airfields with parallel runways. Also turning the aircraft to early may delay the eventual capture of the desired path and result in an undesired over flight of obstacles or protected airspace. Therefore, novel systems and methods which reduce or eliminate overshoots during localizer reposition maneuvers would have utility.